1. Field of the Invention
The present invention relates to a Pulse Width Modulation (PWM) controller, configured to protect power terminals or signal lines against shorts that may occur in a motor controller, without requiring a separate element to do so, thus decreasing the price of the motor controller and improving the reliability of the motor controller.
2. Description of the Related Art
Motor controllers, which are currently used for the blower motor or the like of a vehicle, are of the linear control type and typically perform control using a single large-capacity Field Effect Transistor (FET). Since these motor controllers have a large-capacity FET, they are designed so that even when a short circuit occurs in the power line and the signal line of an FET controller, the FET is not broken down and the internal temperature element thereof, however, is broken down.
Further, since these motor controllers use only a single FET, they have a simplified configuration and are easily controlled. However, the power dissipation increases in these motor controllers. When power dissipation increases, fuel efficiency decreases during operation of, e.g., an air conditioner. Thus, research has been conducted into an object which is able to reduce power dissipation and improve fuel efficiency using a Pulse Width Modulation (PWM) control scheme. When a PWM control scheme is used, however, in a motor controller, the price of the overall controller increases, because a short circuit protection function must be applied using an FET which has a suitable capacity and logic instead of a large capacity FET. FIG. 2 is a graph illustrating the current flowing through a PWM controller and FIG. 3 is a circuit diagram illustrating a conventional PWM controller. Referring to FIG. 2, the current may have a normal state, an overcurrent state and a short state. As can be seen from the graph, the current of the PWM controller has the tendency to increase depending on the duty ratio. As shown in FIG. 3, when both terminals of a motor are short circuited because of worker error or the like, an overcurrent flows therethrough and then a low-side FET L may burn when the low-side FET L is turned on. Therefore, when it is determined by a current sensor that an overcurrent is flowing therethrough, the low-side FET L must be forcibly turned off during the time period in which the low-side FET to L can resist the overcurrent. Typically, this time is several tens of microseconds or less. Therefore, a method of stably implementing such an overcurrent protection circuit at a low cost is required.
The foregoing is intended merely to aid in the better understanding of the background of the present invention, and is not intended to mean that the present invention falls within the purview of the related art that is already known to those skilled in the art.